This proposal is aimed at an investigation of control of DNA replication in normal and noeplastic tissue. Four major approaches will be used. First we intend to purify a low molecular weight DNA polymerase operating in the nucleus and distinctly different from other DNA polymerase activities found in the cytoplasm. This polymerase is a likely candidate for the replicating enzyme. If purification is possible, the activity as well as the molecular structure of the enzyme derived from hepatomas and from host or normal liver will be compared. Secondly, we intend to investigate the chemical composition of the nuclear membranes in liver and hepatoma cells. The nuclear membrane might be involved in the control of DNA replication and differences in the composition of the nuclear membrane derived from hepatoma or host liver cells might help to understand some aspects of the control process. Thirdly, we would like to separate the components making up a possible replicating complex. The main constituents of such a complex are beleived to be DNA, enzyme, and membrane components. If separation is possible, a restoration of such a complex will be attempted. Fourthly, the effect of cytoplasmic components or humoral factors on DNA replication will be investigated. There is evidence that such factors play a role in control of growth and DNA replication. By using factors from hepatoma tissue or tumor-bearing animals on nuclei or cells of normal liver, or factors from normal animal on nuclei or cells from hepatomas, we hope to obtain evidence for the involvement of such factors in control of DNA replication.